BETA-BLOCKADE AS AN ALTERNATIVE TO CARDIOPLEGIC ARREST DURING CARDIOPULMONARY BYPASS

Background. As an alternative to cardioplegic arrest, cardiac surgical conditions have been produced using beta-blocker-induced minimal myoc ardial contraction (MMC) during cardiopulmonary bypass. The technique of MMC involves the use of high-dose intravenous esmolol to suppress m yocardial chronotropy and inotropy sufficiently to produce cardiac sur gical conditions. The purpose of this study was to compare conventiona l crystalloid cardioplegic arrest with MMC in terms of ischemia avoida nce, myocardial edema formation, and cardiac function. Methods. Twelve dogs were placed on cardiopulmonary bypass. Six dogs were subjected t o crystalloid cardioplegic arrest for 2 hours. Surgical conditions wer e produced in the other 6 dogs for 2 hours using intravenous esmolol w ithout aortic clamping or cardioplegia. Arterial and coronary sinus la ctate concentrations were determined as a gauge of myocardial ischemia . Myocardial water content was determined using microgravimetry and pr eload recruitable stroke work was determined using sonomicrometry and micromanometry. Results. Significant lactate washout was demonstrated after cardioplegic arrest but not after MMC. Myocardial water content was significantly less during and after MMC compared with cardioplegic arrest (p < 0.05). Preload recruitable stroke work was decreased comp ared with baseline values in both groups (p < 0.05). Conclusions. In c ontrast to a previous study that involved 1 hour of MMC, in this study , ventricular function was decreased to the same extent as with cardio plegic arrest after 2 hours of MMC. This was attributed to the accumul ation of ASL-8123, the primary metabolite of esmolol, which possesses beta-antagonist properties. Although postbypass ventricular function i s similar in both groups, MMC appears to be superior in terms of ische mia avoidance and myocardial edema formation. (C) 1998 by The Society of Thoracic Surgeons.